#include<fstream>
const int white=0;
const int gray=1;
const int black=2;
const int tree=0;
const int back=1;
using namespace std;

ifstream f("ciclueuler.in");
ofstream g("ciclueuler.out");

int n,m,i,j,color[100001],viz[500001],type[500001],grad[100001];
struct lista
{int nod;
 int index;
 lista* next;};
lista* a[500001]; 

void add(int xx, int yy, int ind)
{lista* q = new lista;
 q->nod=yy;
 q->index=ind;
 q->next=a[xx];
 a[xx]=q;}


void depth(int x)
{lista* q=a[x];
color[x]=gray;
while(q)
{if(color[q->nod]==white && viz[q->index]==0)
   {viz[q->index]=1;  depth(q->nod);
    type[q->index]=tree;}
 if(color[q->nod]!=white && viz[q->index]==0)
  {viz[q->index]=1;
   type[q->index]=back;
   }
q=q->next;}
color[x]=black;
}

int conex()
{for(j=1; j<=n; j++)
     if(color[j]==white)
       return 0;
 return 1;      
}

int eulerian()
{
 for(j=1; j<=n; j++)
    if(grad[j]%2==1)
       return -1;
   return 0;         
}   

int sx,sy,nextx;

void eulerian_path(int x)
{
lista*q;
lista* w;
m--;
while(m)
{q=a[x];
while(q)
{if(viz[q->index]==1)
   {w=q;
    if(type[q->index]==back)
        break;}
q=q->next;}

nextx=w->nod;
sx=x;
sy=w->nod;
viz[w->index]=2;

g<<sy<<" ";
x=nextx;
m--;}

}

char buff[50],nrc;

int get_number()
{int nrn;
nrn=0;
while(buff[nrc]<='9' && buff[nrc]>='0')
    {nrn=10*nrn+buff[nrc]-'0';
     nrc++;}
return nrn;     
}

int main()
{f>>n>>m;
int aa,bb;
f.getline(buff,50);
for(i=1; i<=m; i++)
  {nrc=0; 
  f.getline(buff,50);
  aa=get_number();
  nrc++;
  bb=get_number();
  add(aa,bb,i);
  add(bb,aa,i);
  grad[aa]++;
  grad[bb]++;}
depth(1);
if(conex()==0 || eulerian()==-1)
   g<<"-1";
else   
{
g<<"1 ";
eulerian_path(1);
}
f.close();
g.close();
return 0;
}